Labradorite’s ‘Blue Rainbow Moonstone’

September 1, 2001byGary Roskin

Okay, so it is, and it isn’t. Yes, it is labradorite. No, it isn’t really the mineralogically true “moonstone,” although that doesn’t keep most of the jewelry trade from calling it that. The proper varietal moonstone is an orthoclase feldspar, so the labradorite feldspar’s so-called variety “blue rainbow moonstone” isn’t too far from the correct branch of the family tree. The difference between labradorite “moonstone” and orthoclase moonstone isn’t obvious, which results in the name-calling and mineralogical confusion among dealers and gemologists. Technically, “blue rainbow moonstone” is a misnomer, but a very popular one.

History and romance. The original moonstone—orthoclase moonstone, the one jewelers and consumers are most familiar with—is a translucent to semitransparent cabochon-cut gem with a white or blue billowy light. It can be white, orange, brown, or gray. You can find a fair number of orthoclase moonstones carved into moon-faced cabochons.

Because of its moving internal light, some wearers in the East believe moonstone has a living spirit within, one that will bring good fortune. It’s considered a sacred stone that gives the wearer the power to read the future. Along with alexandrite, orthoclase moonstone is pearl’s alternate birthstone for the month of June.

Fifteen years ago, a new “moonstone” came onto the market. It was discovered in southern India in a small mining area amid rice fields. (Orthoclase moonstones come from Sri Lanka as well as India, Burma, Madagascar, and other countries.) This discovery—which has been identified chemically as labradorite feldspar—has either a blue sheen, called royal blue in the trade, or a multicolored sheen, which the trade calls “rainbow.”

Dr. Henry Hänni of the Swiss Gemmological Institute (SSEF) in Basel was the first to publish the chemistry and identification of the new “moonstones.” Mineralogically, Hänni argues, these gems are not true moonstones, since the billowy light doesn’t come from reflections off albite inclusions, as is the case with the orthoclase moonstone. The labradorite moonstone gets its effect by reflection off twinning planes, a common optical phenomenon of most transparent to translucent labradorites. This is the same phenomenon responsible for the colorful look of multicolored opaque to semitranslucent spectralight labradorite from Finland. Spectralight, as well as the traditional labradorite from Labrador—both commonly seen as huge tablets used for walls and countertops—get their dark gray body color from ilmenite inclusions. Labradorite moonstones do not contain ilmenite and therefore look like the milky orthoclase moonstone. Hence the confusion: It looks like moonstone but has the colors of labradorite.

“People who use the term ‘labradorite moonstone’ or ‘rainbow moonstone’ are on a ‘red emerald’ track,” says Hänni. “The historical and global agreement of the term ‘moonstone’ is used only for orthoclase. Labradorite is not a moonstone.”

Moonstone is a potassium sodium feldspar. Gemologically, it has a lower refractive index and lower specific gravity than labradorite. Blue and white are the only colors for a moonstone’s sheen—there is no yellow, orange, or purple.

Labradorite, on the other hand, is a calcium sodium feldspar. It’s also called spectrolite because it produces spectral colors. These colors are produced by interference and diffraction off labradorite’s peculiar lamellar (flat plate-like) growth, not by scattering off albite inclusions. Labradorite has a higher RI and SG than orthoclase moonstone.

“The composition, identification values, and the reason for the light effect are different between moonstone and labradorite,” says Hänni. “There is no reason—except commercial—to call labradorite a moonstone … it’s confusing, and incorrect.”

(Note: The Gemological Institute of America’s Gem Trade Laboratory acknowledges the trade’s use of the misnomer by making its identification conclusion as “Labradorite—known in the trade as rainbow moonstone.”)

But inclusions are what cause the rainbow effect. “Inclusions break up the light, and we have spectral colors,” says Nichani. “When there are more inclusions, that’s when the rainbow effect comes into play.” Fewer inclusions mean fewer colors. “Nice and clean, transparent to translucent, good clarity—that’s when the stone is blue.”

Color variations. Royal blue appears to be the most popular color, and today it’s the “darling stone” of the designer trade. “It used to be a healy-feely stone,” says Nichani. “Now, it’s set with platinum and diamonds.”

When it was first reported in the 1960s, rainbow moonstone was incorrectly labeled “water opal” because of its transparency and multicolor sheen. While there is material that shows just one or two colors in translucent cabochons, semitransparency with numerous different colors of sheen distributed evenly across the stone is preferred.

Enhancement. Currently, there are no enhancements to alter the clarity or color of labradorite moonstone.

Pricing. There’s not a lot of material available, so size plays a big role in pricing. Material that’s 7 x 9 mm, 8 x 10 mm, or 3 cts. and up is rare and commands a higher price. Expect to pay at least $100 per carat for stones heavier than 5 cts. For stones under 5 cts., prices can range from $45-$100 per carat.

Care and cleaning. Labradorite blue rainbow moonstone has a hardness of 6-6.5, which may seem somewhat soft for wear. But designer Conni Mainne of Healdsburg, Calif., points out that since it’s not a brittle stone, it holds up well. In fact, if you were to look back in history, there was plenty of orthoclase moonstone (same hardness) used in Victorian times, and we see these jewels in fine condition even today.

“Cleaning is no problem, for a change,” says Mainne. “Water, ultrasonic solutions, whatever. [But] they are soft stones, and will abrade over time.” Avoid letting the stones rub against other jewels.

Bench repair and setting. Any feldspar is easily bruised by metal tools such as chasing tools, burnishers, and reciprocating hammers. Mainne uses a reciprocating hammer and finishes the stone off with chasing tools. She also cuts a little bearing in the bezel so that it will fold down neatly, especially when the setting is cast and thick.

Scratches can be polished out “without taking the stone out of the setting,” says Mainne. During ring sizing, Mainne strongly advises that you suspend the stone under water with a third hand to help prevent damage.